1.Field of the Invention
This application claims priority to France Application No. 10/55363, filed 2 Jul. 2010, the entire contents of which is hereby incorporated by reference.
This invention relates to the domain of the suppression of the DC component inherent in any radio frequency chain. More particularly in a radio frequency reception device containing an analogue stage to process the signal received from a digitisation of this signal.
When a signal is transmitted by radio it is generally modulated and carried by a “carrier” frequency. When the signal is received, the carrier is removed to provide a “baseband” signal. The signal is amplified and the DC component is reduced to a minimum before the signal is transmitted to the digital receiver. This type of transmission is used, for example, in the field of mobile telephony, Wi-Fi, Bluetooth and other transmissions.
FIG. 1 describes a simplified diagram of this reception. A radio frequency 1.1 is received by the device. It is then processed to remove the carrier by the block 1.2 which provides a baseband signal 1.3. This signal is transmitted to an analogue stage 1.4 intended to carry out an initial analogue processing on the signal. This analogue stage is composed of a multiplicity of analogue components that can, exactly like block 1.2, insert a DC component in the signal passing through these stages. This processing can include filtering but often consists of an amplification of the signal received. This amplified signal 1.5. is then digitalised by an analogue digital converter 1.6. to give a digital signal 1.7 before being transmitted for processing to a digital stage 1.8 depending on the type of device.
The different components of the analogue stages 1.2 and 1.4 are at the source of the appearance of a parasite DC component. The appearance of a DC component originates inter alia through the disparities of analogue components used in the construction of differential stages. The stages carrying out amplification functions should naturally be painstakingly elaborated to avoid successive amplifications of the DC component saturating the analogue-digital converter downstream of the analogue chain. Such a component, even if with a low range, will continue to subsist regardless.
In practical terms, it can be observed that, without processing, these DC components can saturate amplification stages and the converter.
It is therefore indispensable to offer a processing system to remove all or part of the effect caused by these DC components before the converter.
2.Description of Related Art
It is known to carry out in a steady state a retroactive low-pass filter loop to provide compensation at a single point of the analogue chain. This method raises the issue that if the compensation point is at the end of the analogue chain it is still possible for a previous amplification stage to be saturated. On the other hand, the DC component to be corrected is amplified by all the amplification stages and can be significant at this level. If the number of amplifiers of the chain increases, a single compensation point can turn out to be insufficient to avoid saturation upstream and downstream of this point.
The invention aims to resolve these aforementioned problems by a compensation process of the DC component inherent in any radio frequency chain allowing us to determine a set of multiple compensation values from a single measurement, generally situated in the digital stage that must be applied at multiple compensation points of the analogue chain. The compensation points are calculated by an iterative process converging towards a cancellation of the DC component and avoid saturating the amplification components and the analogue digital converter.